Dielectric testing-method and means



- Dec. 29; 1942. I I R. L. DAVIS 2,

DIELECTRIC TESTING-METHOD AND MEANS lFi l ed Oct. 2s, 51 941 I 2 Shets-Sheet 1 fF' l (3. l.

I 'A.C. 25 L I SUPPLY LIN E INYENTOR.

R; L..-'D AV IS 2,306,529 DIELECTRIC TESTING-METHOD AND MEAN' 2 Sne Sheet 2 Y Dec. z9, '1942.'

Filed oct. 28, 1941 Patented Dec. '29, '1942 mum-mo i'ijtalph nn via' wsummracmn Ifippncflhh w en. 194d, No. 416359 I $5 inawa. 175183)- inventionrelates to novel apparatus ,ior

- and methodsof testing ignition systems and more specifically relates to novel apparatus for and methods of testing. the I ignition systems Io'ff airplanes,iautomobiles, and of sparkplugsand iorf determining-thei -existence t electrical .iaults in u h systems.

The distributorand the conductors extending;

from the segments oivthe distributor of an ignition system of anairplane are usually mounted in back otthe engine. and accor ingly are very dimcultto reach. The. dielectric'conditions of' theconductors of the distributor must be constantly tested 101: any short circuits or other tailures which may occur, since such failures will cause a corresponding failure of, the ignition, at

the spark plug and therefore of I that particular cylinder oi theenginep, i A I i Heretoforano practicalmeans has been avail ableri'or testing; the dielectric condition of the distributor system.

Accordingly, w an object of my invention als to provide novelapparatus" for and methods of;

testingth'e distributor system oi: the ignitionsysteam. I

A ilurther object of my inventioniis to provide a' novel method for simultaneously testing all of the conductors of the distributor system ior the determination 01a dielectric fault.

Still another object of my invention ispto pro vide a novel methodof simultaneously testing the 30. Figure 1 is asch'ematic circuit diagramot' a distributor system for dielectric fault and for thereafter individually testing each electrical system individual to each of the spark plugs.

Still another object not my invention is to provide novel apparatus-and methods of testing insulation resistance of the ignition system. I

Still a further object of myinvention is to provide a novel method attesting dielectric and insulation resistance oi. an ignition system. it

In addition to a careful test of: the ignition system, it'isalsoimportant to test the condition of each individual spark plug not only ior'its breakdown voltage, which is important; but for the possible existence ot sneak" currents whichmay have been created by the accumulationlot.

conducting materials which may produce a leakage current by-passing the spark plug terminals.

In such a case although sparkdischarge may beproduced across the plug terminals, when sumcient voltage is applied, its.;strengthfiis con-'- siderably reduced due to the-fact that a by-passl exists i'orvsome of the currentwhich normally I shouldha'veflowedthrcughthe spark gap; I In accordance with my invention, thetollowv ns spark plug is made; The (spark ina a transparent envelope, preferably or glass filled'with' a gas, iorin'stanceCtoz 'at ai'pressur'e'f simulating the press'urein an Qairplan'e engine cylinder durinig the lnstaritof breakdownbl the." spark plug. Voltage isjthenapplied to'thefspa'rk plug corresponding to that whichis appliediinan engine andthe spark is then observed."

a ki- "x 1 p Figure v4 is a 'cross sectional'=-view showing an adaptation oi'tmyginverition ior-testingsthe ima perviousness of insulating coating, on a con- The voltage on the secondary is now-' chang ed and the operator-observes ,not'onlythe mum:

"tion at the terminalsiof the spark' plugbutjalso v .the ,conditionfadiacent to it for. any evidence'otf.

leakage currents. i A milli-arnmeter 'employed'as-described herein 1 7 after provides'indications oi snysueniesxa e; currents'at varying-ranges oi voltages belo'w'ithej breakdown voltage-ot,. the spark plug."

Accordingly, an! object or my; invention i to provide novel apparatus for andmetho'ds of ing spark plugs. v 3

Still another object of'the present invention. is the provision ot means for; determining whether a coating oisrubberv or other-insulating; material on conductivefmaterial is continuous and'irnpervious, I I v a These andfmany othe'nobj'ects of my invention will" pp t. and w er n app t-L pointed out in the r newing description ans preferred embodiment of my mvenuam,

Figure 2 is'a schematic vievvvpart yrmlperspec-s tive ,of the testing electrode about" to placed ontact withrthe-distributor segmentsfot an! n s a, I v Figure 3 isTa cross-sectional viewg'shovvin adaptation 'oi f my invention tor testing'f tainer o1 conductiveematerial'.

' Referring now to lligure te s-1m them I itiating relay ll whichc'ontrols the energijsat'ion-C oi the systemin the manner to be'describedhere' dn ter i n rsi d: d t m 13 are? at their back contact positionlunder the action otspring; ll, H

trolled by (push button l. I; gnon'nally the nductin por n .b mu u n "P. d h d 1 ot engagement withflcontacts 'ii'land l1 bythe), actionot springilmneend 01; which is tothe 'nxed'ring ll haying a slotthrough which t for jdeterminingfthe conditionoffthe" pin 29 extends. The other end of the pin 20 carries the conducting head 22 of the push button l and the entire switch is held in disengaged position by the spring pressure against the disk 22 and fixed ring I 9.

In order to initiate operations the operator will momentarily depress the push button |5 to bridge contacts l6 and I1 whereupon a circuit is completed for the relay over a circuit from the 115 volt A. C. supply line 23 over conductors 24 and 25, bridged contacts I5 and I1, bridged by the conducting dome 22 of push button l5,

conductors 25 and 21, to the windingof relay and thence over conductor 3| to the return lead 33 of the supply line 23.

Relay II is thereupon energized and operates its armatures l2 and I3 from their back contactv position to their front contact position at which they engage contacts 34 and 35. The engagement of armature |2 with contact 34 provides open the locking circuit for the relay II, when an electrical fault in the system being measured is discovered, by moving its armature 39 from the position shown to disengage contacts 4| and The energization of relay II also completes an energizing circuit for the primary winding 43 of the transformer 44, the circuit extending from the voltage supply 23 over conductor 24, armature l2 and its front contact 34, conductor 31, contacts 4| and 42 bridged by the armature 38, conductor 45, conductor 46, primary winding 43, tap switches 46 and 41, potentiometer 48, conductor 49 to the front contact and armature l3 and over conductor 33 to the source of supply.

It will be noted that this circuit which enersizes the transformer 44 is completed not only over the front contacts of the initiating relay II but also depends on the back contacts of the fault finding relay 39 so that this circuit is initiated by the energization of relay II and will, as hereinafter be apparent, be terminated upon the instant a fault is detected.

The voltage across the primary winding 43 of transformer 44 is controlled by the resistance inthe potentiometer 49 determined by the position of tap switch 47. The ratio of turns be-. tween the primary winding 43 and the secondary winding 5| of the transformer 44 and therefore the step-up voltage will be determined by the is arranged to detect a fault in a manner to be described. The conductor 56' has a contact face 56 for this purpose. 7

The opposite terminal 53 of the secondar 5| 5 extends over the conductor 58 and through the button 92 provides a by-pass circuit around the ammeter whenever tests are made which are for the purpose solely of detecting dielectric failures and not merely leakage currents, as in such case the instantaneous current flow on a short circuit may burn out the ammeter if permitted to flow 1 therethrough.

- The distributor is is provided with a series of taps 53 and 54 so as to further regulate the,

ratio of turns winding.

Connected across the terminals'of the portion of the secondary which is employed in the system is a voltage transformer 55,;one'terminal 56 of the primary of which is connected to the brush termnal 51 and the other terminal 33 of which is connected to the terminal 53 of the secondary 5|.

The secondary winding 59 of transformer is connected across the volt meter H to provide of the primary and secondary indications of the voltage across the terminals of the secondary 5| so that the operator isconstantly apprised of the test voltage being applied. In the alternative a volt meter may be connected across a portion of the primary 43 of the transformer 44. This volt meter will give a reading in proportion to the voltage in the secondary circuit and may be calibrated to read accordingly.

Normally. before any-testing operations are performed, switch 12 is closed and completes an energizing circuit for the horn or loudspeaker 13 of any well known construction, the circuit extending from the power supply 23 over conductor 24 through the armature l2 in engagement with its back contact 14 and through the winding of the horn 13 to the return circuit over conductor 15.

A parallel circuit is also completed through the lamp 15 so that upon the closing of the switch 12, the horn 13 produces an audible sound in a manner well known and the lamp I4 is illuminated, indicating that energy is being supplied from the source and the tester is ready for operation. I H

In order now to operate the system. for testing, the operator depresses the pushbutton l5, completing an energizing circuit for the initisiting, relay H as described hereinabove.- Initiating relay upon energization locks itself and deenergizes the circuits for the horn 13 and lamp 1! as armature I2 leaves its back contact I4, and aisocompletes an energizing circuit which extends the energy from the source of supply through the primary. 43 of the transformer 44 to i the tester 55.

A visual indication-of the energization of pri mary 43 is provided by the lamp 49, which is connected across the transformer as will be evident from the circuit diagram. 5

The potential is now applied to the testing contact 59 ofthe tester 55 and it is now ready to be connected to the conductor whose insu- 2,soe,t29' r for the hornet audible. indicating means l3 and Q .Just recedin thea a x lation Is to be'tested p g -for"the'visuallainp I! soasfto provide an'aud ble plication of the, tester; for testing the insulation. v the tap switches 46;" and 53 have beensposie tioned so as to secure thedesired voltage as indicated on either voit e'terjas or," (depend a ing on whichis used) .at the testingelectrode 56.

In the present-instance, (as'sh'own inFig'. 2). a' simultaneous, Connection is made from. ,the

tester. u to the segments. of t distributor ill of an ignition system. Preceding this the magneto is removed to permit'the test; The ignition systembf -3. 88-S01l118 engine is vschematici'tlly illustrated in Fig. 2 in which a distributor "10. provided. with distributor segments at individual toleach of the 'spark plugs, will be no signal at Wh pth s m nt, is illustrated. The circuit connections to'themagneto have not hjerebeen shown and in fact are removed from the systemduring the testing; operation. The rotatingbrus h is not shown here Extending from'each of thesesegmentslc are, the 'usual individual vconductors 8| which,aiter passing through" the. radio shield extend to terminals 231 (Fig. 3) in the cylinders I02. p h 1 t A A As is wellknown, these conductors are insue lated so as to prevent any by-fpass' circuit, the

return circuit being through'thefopposlte terininal of the plug to ground, as schematicallyillustrated at 208'in Fig. 3.$ In the present illustra-- 'tion .two spark plugs areshownper cylinder as is com'monin airplanepractice. I g b v In the event that there is any insulation .we akness or'breakdown' in' any of the conductors;

their associated sparkplugs will, of course, not" be activated since the current will take "the shorter path to ground provided by the insulation defect, Thatcylinder is therefore non-effective.

The presentdevicefas now be shown," will first simultaneously test all of the conductors tot med dielctflcbondltlons. by applying, varying. I

determine whether there is any such weakness in any of them; and if such a weakness doesshow up, to individually test the circuits until the breakdown has been localized.

To this endthe' magneto system is, as described above disconnected and the spark plugs are l) and then" have anfouternietallic protective moved. Tester 56, Fig. 2, is now brought'into engagement with all of the segments; 8II with the-"system of Fig. 1 energized as describedabove.

If now, the insulation ofall oi. the conductors at to the terminals to which the'tester'il is connected are in good condition; that is to say,

there is'no' fault or grounding of any bi these. v

conductors, -the secondary 5i will remain (open circuitedgi Should; however, there be afault inany one of the ignition circuits d'ue to the i act through the fault to ground, returning over the relay 39 and-throughconductoril, closed switch 62 and conductor 58 to the'oppositeterminal' ill of the secondary 5|. The currentflowi'ngin this circuit will be sufllcient to energize relay" which will operate its armature" against theaction of spring 38" to disengage contacts 4| "and '42;

, Disengagement of contacts 4| 'and=-42will'open the energizing circuit to the transformer thereby instantly terminating current flow over the short circuit and'iwill also deenergize' relay ll so that .it's armaturesH-and'l 3 drdp'to theirback contact position under the-action-of spring" H. Armature H in engagementwithitsxback of individual spark plugs and 'yis'ual indication or "the existence offa fault. It is fnowjnecessary to indivduaily "test j'ea ch of test electrodejS having a substitutetestingfg face 56fof anyf's'uitablesiz'e is '(as seen in Fig. 1)

applied iindividually' 'suocessivelyftq each of,

10 the uistributptsegments toftthe i nition system. lneeachinstan'c'e', the bush 1 button i 5 is closed to initiate operationsand'te'sting is performed h am QI Q fib l' when 1 -I ists, relay 3! will remaindenerg'ized andfthere containing the tiaulty conductor is reached, the same short? circuit as described, above will occur a ams ih iv ve macaw s s e abov to its open position. In such a case'where leakage currents flow through weakened insulation? although theleakag current flowing maybef insuflicient to'energize relay, 'suchi currents.

- will be indlcated'on themillhamnietenHfwhich so has'a range of currentindications fondetecting} such leakage currents and my; depending upon the leak-ages to fbe measured; range ilO milli-amperes. 1

A further advantage of my systein fli'esidesdn a the fact that'i may measure not only"co inplete dielectric failures where absolute'f'short circuits exist, and conditions whei'e, leakage currents sufficient to; seriously lmpair'l the eilicienc'y of the ignition system exist butr may also detect week;

amounts of voltage to the elctrode'ffl jin' the systemare each covered withfinsulation 90 (Fig covering II: "Inthe eventfof'a dielectrieloss' or breakdown in insulation llLYa current path to described is brought into operation to roduce an indication of this breakdownfl v Auto: the conductors 0| of the ignition system" schematically-- shownin Fig F2) the led ,through aradio Shield 1 oi-fit aihq viuuai' spark iug's in the cylinders IMP ,Duplicate'conductorsll fand spark plugs are usually. used modern airplane engines .to ensure p'ropei ignition. The sperkj 'plugsare' removed prior to 'thetestso that ,breakdowndndication will be caused only bya' defect in the conductors and across the spark plug gap,

metal: sheath 0 I, thus completing the circuit for 5 the relay in the manner previously described} I This flow of current maytend furthertobreak down theinsulation and may, inffact, sparkor is actually preferred; since it thus helps provide a visual indication of the exact pointof, the fault,

and will thus make unnecessary the discarding contact "will complete an ener'gizing circuit of the entirelength of'wi'reg the" distributor [segments toidetermine in which particularcircuit the fault lie's.'j (,To this endthe I When faulty ion a conductor) current will flow between conductor -llflan'd its the. spark plug extends through the In fact, after an indication is given by the ap-. paratus that a particular conductor is at fault and such a pin point or discoloration fails to appear, the push-button ll may be held depressed to cause such a visible burning out to appear at the point of the fault.

It may at times be necessary to perform testing operations at some distance from thecabinet which houses the apparatus. AccordinglyJead 51 to the testing electrode Il may be made as long as desired. "In this case, however, it would be inconvenient for theoperator to return tovv the cabinet to depress push button ll each time it is necessary to reconnect the apparatus after an indication is given.

To obviate this diillculty, an additional push button, Ill is connected in parallel with push button ll and operates in exactly the same man-' ner push button ll.. Push button ill may be m unted on the handle ll of the testing electrode and conductors Ill and III for push button' lll may be ,le'd through the same cable as;

conductoril.

The sperm: may then set the apparatus in operation by depressing push button lll mounted on handle l'when he is at-some distance from the cabinet and thus may test a number of wireswithout returning to the cabinet or may apply' repeated surges of current to a particular wire while simply holding the testing electrode ll.

By the use of the system described in'Hg. 1, it is possible also to test the breakdown voltage of spark plugs and thus to determine whether the individual spark plugs are in good condition. For this purposeusing the system of Pig. 1, the contacting face ll of the testing electrode Ill and thus create a by-pass for the current. Although, the spark plug may spark, its strength may be greatly reduced by such a by-pass. 'Ihus.

although, by observatiolna sparkplug may seem' will be indicated on ammeter ll whenpush-button l! is depressed. The voltage is now grad- I ually raised until'the full voltage of the spark plug is reached. Also, if current'flow is sufilcient (of the order of 5-10 milliamperes) the horn Ii and light "ll of the apparatus'of 'I'lg. 1 will immediately indicate the defect.

If there has'been nosuch dielectric breakdown within the spark plug and the leads therein are well insulated from each other, thenno indication will appear or be heard and the spark Y plug will be found satisfactory.

The importance of such a test is that it will indicate any possible leaks within the spark plug itself which may (while the spark plug is able to spark) reduce the intensity of the spark.

The apparatus herein described may be utilised for various other purposes as, for example, discovering insulation faults in the windings of motors, generators, transformers, etc.

u is electrically connected to one terminal 201 v of the spark plug ill, the other terminal ili being grounded as is common and well known inthe spark plug art. The spark plug is placed in a chamber ill preferably wholly or partly of glass or other transparent material and gas (for instance CO1) is admitted through conduit ill at a pressure equal to the compression reached in an airplane engine'cylinder when the mixture is to be ignited.

For this purpose, the threaded end Ill of the spark plug is screwed into a threaded opening in the base Ill of chamber ill and gas is admitted as described just above. Terminal ill of the spark plug Ill is connected to threaded end ill and is thus grounded through the me,- tallic base ill of the chamber. Terminal ill of p rk P g and terminates in member ili.

' With switch 62 by-passing the'ammeterll,

switches 12 and ll are closed to energize the tester. Contacting .face ll of testing electrode ll is then applied to the end ill of terminal ill the output voltage of the testing apparatus being adjusted by brushes ll, 41 and ii as described above to the rated operating voltage of the spark plug. The sparkis observed through the glass envelope of chamber ill. Thespark plug may fail to spark entirely owing to-a' dielectric break-down within its structure or the spark may be obviously weak for the same reason; or sparking may be observed at points other than at the desired point of sparking. In the operation of an airplane engine, conductive paths for -sneak" currents in the spark plug may be created by accumulation of conducting materials which may produce leakage currents by-passing the spark plugterminals.

Thus, for instance, in various types of battery containers which are frequently made of metal which may be corroded by acids, a protective coating is placed on the interior of the container to prevent such corrosion. Such protective coating. .as' for instance rubber, is normally an in sulating material as well. I

In Fig. 4 I have shown in schematic form a cross-sectional view of a'batte'ry container consisting of an outer metal container ill having a rubber lining ill;

Any breakdown anywhere in the rubber lining will permit the acids to come into contact with the metal and corrode the same.

The testing electrode ill having a brush type contacting face ill may be connected to the apparatus of Fig. l and the metallic brush ill may be swept over the inner surface ill of the container. .Whereverthe lining ill islworn or has been perforated suihciently to substantially decrease the electrical resistance normally oilered by the lining ill suillcient current will flow through the secondarycircuit as previously ,described to actuate the relay ll and produce the aural and visual indication previously set forth.

Obviously, of course, the modification of Fig. 4 is not limited to merely battery containers, but may be utilized for testing any kind of container or structure having a metal lamination and an insulating lamination. 5

In the foregoing I have set forth a preferred embodiment of. my invention together with a series of preferred adaptations and uses, therefor.

-Many variations in the form and construction of m invention should now be clear to those skilled in the art, and many other uses in connection with, the testing of many other devices Such materials may collect along the insulation 16 should also be obvious.

Since my invention is capable of various embodiments and various uses, I prefer to be bound said contacts ffor connection; individual spark not by the specific disclosures by theappended claims. f I

Inc-181m: I J l. Inasystem for detecting, electrical faults in herein, but only an engine ignition systemhaving a distributor withaplurality of contacts and having electrical connections extending individually from each of said contacts for connection to individual spark plugs, means for simultaneously applying a v potential of the order of that'normally applied. to' said circuits when in operation; and means operative in the event that a fault exists in anyone of said circuits for indicating saidfault f. I

l 2. In a system for detecting electrical faults in any engine I nition system having a distributor with a pluralityoi' contacts and-having electrical connections extending. individually from eachof, said contacts for connection to individual spark plugs, means for simultaneously applying a potena tial of the order of that normally applied to said;

l s. m for i wj. v a l n a otential; oi', the order of thatnormally? applied to" said circuits whenin operation; means operative in the event that a fault exists- 1 1 onscre n circuits .for. indicating said fault; 'andmeans for m aflm 81d testing e smea e 8.;In asystemfor'detecting electrical faults in .an engine. ignition systemj'having" a distributor with a plurality of bntacts and having electrical connections,. extending individually can each of said contacts for connection to individual spark p uss; ea o a eous a pl n a n0- tcntial oi 'theord'er of that' normally applied to said circuits when in operation means operative in the event that a fault exists inany one 'ofsaid circuits for. indicating said fault; andmeans for indicating the potentialflbeing applied' to saidtes't circuits when in operation; and means responsive I to dielectric failure in any one of said a electrical circuits for indicating the existence of the failure.

3. In a system for detecting electrical faultsin an engine ignition systemhaving a distributor with a plurality of contacts and havingelectrical;

connections extending individually I from each of said contacts for connection ,to individual spark plugs, means for simultaneouslyapplying a potential oi the-orderoi that normally applied to said circuits when in operation; means operative inthe event that a faultexists in'any oneof said circuits for. indicatingsaid fault and means for simultaneously disconnecting the source ofpotential from said circuits.

4. Ina system for detecting electrical faultsin an-engine ignition system having adistributor with a-plurality of. contacts and having electrical connections extending individually-from each of said contacts for connection to individual spark plugs, means. for simultaneously applying apotential of the order of that normally applied to with a plurality or contacts and having electrical said contacts for connection to individual spark plugs, means for-simultaneouslyapplying a potential of the order of that normally applied to said circuits-when inoperation, said means comprising a source of low voltage and a step-up current limiting transformer;. andmeans operative in the event that a fault existsin any one of said circuits for indicating said fault.

6. In a system for detectingelectricalfaults in an engine ignition systemhaving a distributor with a plurality of contact-sand havingelectrical connections extending individually fromeach of said contacts for connection to individual spark plugs, means for simultaneously applying azpotential of the order of that normally applied to said circuits when in operation: means operative, in the event thata fault exists in any one of said circuits for indicating said fault: and means for thereafter individually testing each of said circults for said fault. I

-7. In a system'i'or detecting electricalfaults in an engine ignition systemhavinga distributor with aplurality of contacts. and having electrical connections extending individuallyfrom each 01'.

9, Ina system for detecting the-electrical faults ini'an engine ignition systm-having a' disftrlbutor with aplurality 9i contactsjand electrical connection iextending' individually from teach"- of said contactsfor connection to individual spark plugs, means for simultaneously applying a'apoten'tialv oi ,the order of" that normally applied to.

said circuits whenil in operation; means. operative fthe eventthat s faul 'xi t many o ?M 1 v circuits for indicatingsaid ta t; andjmeansfor indicating the insulation resistanceof said cir- 1o. Ina system for detecting netnc rsunsm' an engine ignitionjsystem having a distributor connections extendingindividuallylrom scnpr said contacts forconnection toindividual "spark plugs, nieansfor vsimultan'eously,applying 'apotential of the order of that normally applied to said circuits when in operation; means operative in the'event that affaultexists in anyone of. said circuits for indicating said fault; and means for indicating, leakage currents flowing across-the,insulation coverings of said conductors inJsaidelec tricalcircuits.

11. In a System fordetecting electric'airaultsin anaengineignition system having: a distributor with a plurality of contacts and havingelectrical cpnnecn ns extendingindividuallyfrcmeach' of I said contacts for con'nction to,-individual spark plugs, means for simultaneously applying a po tential of the order otythat'normaliy applied to said circuits when in operation, saidlneans comprising a source, of low voltage and a step-upcurrent limiting transformer; means operative in1the event that ajfault existssin anyone oi saidc ircuits for indicatingjsaid fault; a current indicatorconnected in the secondary oi'said transtormer' for indicating leakage currents flowing in said" cir- 12. The methodoi! testil ig-electrical faulfs'in ignition System which .comprises simultaneously applying potentials ofthe iorder ofxth'qse which the circuits normally ca'i ry' all of ;.c ir'cuits of the ignition. system, providing an iindication ingtheeventthatcm'rent'iiowsin anyoneoi said. v circuits, and thereafter individually. applying voltages to. cachetsaid circuitsfi'or detecting the cii'i cuit in which the fault exists.

12 The methodoi"testinglfilectrical faults, in

an ignition system which c mes-s mian neously applying potentials ostne ordero'i': those which the circuits normally carry to; all ,ofthe circuits-of the ignitionsystem and providing indication in the eventjthat current flows in any one of said circuits.

which may exist whichby-passes th terminal 1 of the spark plug. 7

15. In a system for detecting electrical faults in an ignition system having a distributor hav-'' ing electrical circuit connections extending to an individual spark plug; means for applying potential to the electrical circuit of the order of that normally applied to said circuit when in operation, the spark plug associated with the circuit under test being first removed; and means operative in the event that an electrical fault exists for indicating said fault and disconnecting the source of potential.

16. In a system for detecting electrical faults in an ignition system having connections extending to a spark plug terminal, a source of standard voltage supply, a testing electrode;

means including said testing electrode for applying potential to said connections; means for varying said voltage over a wide range in small increments; means for continuously indicating the voltage applied to said connections;'means for instantaneously indicating a fault in said ignition system.

1'1. In a system for detecting electrical faults in an ignition system having connections extending to a spark plug terminal, a source of stand-.

ard voltage supply, a testing electrode, transformer means connecting said source of supply to said electrode; means including said transformer for applying potential from said source to said connections through said testing electrode varying in small increments; and means for instantaneously indicating a fault in said ignition system; and means forcontinuously indicating the varying voltage applied through said testing electrode.

18. In a system for detecting electrical faults in an ignition system having connections extending to a spark plug terminal, a source of standard voltage supply, a testing electrode; means including said testing electrode for applying potential to saidconnections; means for varying said voltage over a wide range in small increments; means for continuously indicating the voltage applied to said connections; means for instantaneously indicating a fault in said ignition system; and means for indicating leakage current flowing in said ignition system.

19. In a system for detecting electrical faults in an ignition system having connections extending to a spark plug terminal, a source of standard voltage supply, a testing electrode; means including said testing electrode for applying potential to said connections; means for varying said voltage over a wide range in small increments; means for continuously indicating the voltage applied to said connections; means for instantaneously indicating a fault in said ignition system; said last mentioned means comprising a relay responsive to fault current flowing in said ignition system; said fault relay being connected on the ground side of said testing circuit.

20. In a system for detecting electrical faults in an ignition system having connections extending to a spark plug terminal, a source of standard voltage supply, a testing electrode, a circuit including said testing electrode, a relay connected on the low potential side of said circuitfor controlling the application of potential from said source of supply to said testing electrode circuit, and means whereby said relay instantaneously disconnects said sourceof supply from said testing electrode circuit in the event of an electrical fault in said ignition "system;

21. In a system for detecting electrical faults in an engine ignition system in which the spark plug and the magneto have first been disconnected; a source-of standard A. C. voltage supply, a testing electrode for making contacts with the ignition circuit to be tested; circuit connections including transformers from said source of supply to said testing electrode;-mea ns including tabs on said transformer for varying the voltage applied to said testing electrode from said source in small incrementsover a wide range of voltages; relay means connected in said circuit from said'source of supply to said testing electrode and responsive to fault currents flowing in said igni-. tion circuit in the event of a fault therein; a milliammeter in said circuit from said source of supply to said testing electrodefor indicating leakage currents in said ignition circuit; said relay means and mllliammeter being connected in the ground side of said testing circuit.

22. In a system for detecting electrical faults in an engine ignition system in which the spark plug and themagneto have first been discon nected, asource of standard A. C. voltage supply, a testing electrode for making contacts with the ignition circuit to be tested; circuit connections including transformers from said source of supply to said testing electrode; means including tabs on said transformer for varying the voltage applied to said testing electrode from said source in small increments over a' wide range of voltages; relay means connected in said circuit from said source of supply to said testing electrode and responsive to fault currents flowing in said ignition circuit in the event of a fault therein; a milliammeter in said circuit from said source of supply to said testing electrode -for indicating leakage currents in said ignition circuit; said, relay means and milliammeter being connected in the ground side of said testing circuit; and

means controlled by said relay means in response said transformer for varying the voltage applied to said testing ,electrode from said source in small increments over a wide range of voltages; relay means connected insaid circuit from said source of supply to said testing electrode and responsive to fault currents flowing in said ignition circuit in the event of a fault therein; a milliammeter in said circuit from said source-of supply to said testing electrode'for indicating leakage currents in said ignition circuit; said relay means and milliammeter being connected in the ground side of said testing circuit; and means for continuously indicating the voltage supply to said testing electrode.

24. In a system for detecting electrical faults in an ignition system having connections extending to a spark plug, a source of standard voltage supply, a testing electrode; means for applying potential varying in small increments; means for instantaneously indicating a fault in said testing circuit; and remotely operated means for controlling the connection of said circuit from said source of supply to said testing electrode.

25. In a system for testing the dielectric conditions of a spark plug, an envelope containing 

